The Beseler Topcon was a sytem camera back when 35mm SLRs were in their hayday. As I remember that along with Mirandas and those newer-style Exactas and a few others, they formed a second tier under the Nikkormats and Ftbs. They were less expensive but their systems while pretty extensive didn't extend into the Pro high-end like Nikon with the F or Canon with the F1.